This invention relates to a method of dry etching suitable for etching a single monolayer of atoms or molecules or a few monolayers of atoms or molecules on a substrate to be etched.
More and more minute forming is being required of large scale integrated circuits (hereinunder referred to as "LSI"). In order to cope with this growing tendency, a method of utilizing photo-induced chemical reaction as a new etching technique has been given much attention. Why this expectation is entertained of the photo-induced process is considered to be mainly because it allows a low temperature process to be realized, it can reduce the incidence of damage on substrates to be etched, and, in addition, it enhances selectivity in spacial reaction, such as, for example, the enablement of partial etching of a photo-irradiated area solely. Such photo-assisted etching is described in detail in, for example, "Semiconductor World", 1984, No. 11 on p. 103. In the present state of the art, however, there are many unclear points in relation to the reaction process which proceeds on the solid surface when it is irradiated, and efforts have been made to solve these problems by means of a surface analysis method. For example, in the above-described report in "Semiconductor World", the surface reaction process which is accelerated when the surface of silicon which has adsorbed sulfur hexafluoride (SF.sub.6) is irradiated with a CO.sub.2 laser is estimated on the basis of the data of photoelectron spectroscopy, and the relationship between the surface reaction process and the etching mechanism of the surface of the substrate is discussed.
In the above-described known examples, it has been made clear that the substrate surface is etched by photoactivation of molecules and atoms which have been adsorbed. However, exact control of the depth of etching at a molecular and atomic level has not been considered.